Fiber optic switching apparatus and method

ABSTRACT

A fiber optic switching apparatus includes a first fiber alignment head having a V-groove formed therein. A first optical fiber is mounted in the V-groove with an end of the first optical fiber being arranged to be spaced apart from an end of the V-groove. A second fiber alignment head is arranged to be adjacent the first fiber alignment head. The second fiber alignment head includes a switching member arranged to be pivotable between a first position and a second position. A second optical fiber is connected to the switching member with the second optical fiber being arranged to have an end extending into the V-groove such that the ends of the first and second optical fibers are in longitudinal alignment when the switching member is in its first position and being out of alignment when the switching member is in its second position. The second optical fiber preferably is arranged such that when the switching member is in the first position, a portion of the second optical fiber is bent so that elastic forces in the first optical fiber retain it in the first position in the V-groove.

BACKGROUND OF THE INVENTION

This invention relates generally to fiber optic communications systems.This invention relates particularly to an apparatus and a method forcoupling optical signals from one optical fiber into another opticalfiber.

Fiber optic communications systems employ optical fibers for carryingcommunications signals because such systems have the capability ofcarrying signals on a large number of channels. Such systems arenecessary for meeting the demand for communications channels.

Another advantage of optical fiber communications systems is that fiberoptic transmission lines are capable of guiding signals for both voiceand video transmission in real time. Accordingly, optical fiber isfinding increasing use in applications such as monitoring automaticteller machines and video conferencing.

A fiber optic communications system includes switching stations so thatcommunications signals may be routed between any two locations in thenetwork. Each switching station switches signals carried by one opticalfiber to a selected one of a plurality of optical fibers fortransmission to another switching station in the network.

Systems for switching optical signals between optical fibers includeapparatus for placing the fibers end-to-end so that light may be coupledout of one fiber into the other. Direct coupling between single modefibers is not practical. Therefore lenses are typically used at the endsof the fiber. A first lens expands the light beam output from one of thefibers. A second lens collects the beam output from the first lens andfocuses it on the end of the second optical fiber. The use of lenselements makes the coupling device complicated, large, unstable andexpensive and requires critical alignment. As other light crosses eachinterface between media having different refractive index, signal lossoccurs due to reflections.

The switching station should be highly reliable and have low insertionloss and high return loss. Insertion loss reduces signal strength,whereas returned, or reflected, signals cause cross talk. The fiber endsmust be axially sand laterally aligned and must be spaced apart by onlya very small distance to meet the operational requirements.

Some present fiber optic switching stations us e robots to move thefiber from which a signal is to be extracted to a selected contact pointwhere the signals is coupled into another optical fiber. Robots for thispurpose are very expensive and have problems with repeatability inplacing, the fibers in positions where signals may be satisfactorilyextracted from one optical fiber and input into another. Robots are alsoslow and have limitations on the number of fiber optic channels that maybe used.

Other prior art switching apparatus (e.g. U.S. Pat. No. 4,896,935) usesa stepping motor to place the fibers in alignment for signaltransmission. Stepping motors have the disadvantages of poor resolution,non-uniform stepping and thermal sensitivity.

Another prior art switching apparatus has an input fiber mounted on amagnetic base that may be pivoted to direct signals from the input fiberto a selected one of two output fibers. The base is arranged adjacent apair of longitudinally aligned solenoids. Electrical switching apparatusenergizes one of the solenoids to move the end of the input fiber intoalignment with the output fiber corresponding to the solenoid. The inputfiber includes a lens that directs the optical signals to correspondinglenses at the ends of the output fibers. This device has the drawbacksassociated with the use of lenses to couple optical signals between theends of optical fibers. Other disadvantage of this device are that thesolenoids are large and that the device readily mountable on a printedcircuit board.

SUMMARY OF THE INVENTION

The present invention overcomes problems associated with the prior artby a providing a highly reliable fiber optic switching device thatrequires no lenses or stepping motors. The fiber optic switching deviceaccording to the present invention has low insertion loss and highreturn loss, which makes the invention ideal for use in communicationsapplications. The present invention further has high switching speed,low power consumption, small size and a wide operating temperaturerange. Accordingly, the present invention is suitable for use inapplications such as real-time monitoring automatic teller machinenetworks, redundancy and backup for fiber distributed interfaces andcomponent testing.

A fiber optic switching apparatus according to the present inventioncomprises a first fiber alignment head having a V-groove formed therein.A first optical fiber is mounted in the V-groove with an end of thefirst optical fiber being arranged to be spaced apart from an end of theV-groove. A second fiber alignnent head is arranged to be adjacent thefirst fiber alignment head. The second fiber alignment head includes aswitching member arranged to be pivotable between a first position and asecond position. A second optical fiber is connected to the switchingmember with the second optical fiber being arranged to have an endextending into the V-groove such that the ends of the first and secondoptical fibers are in longitudinal alignment when the switching memberis in its first position and being out of alignment when the switchingmember is in its second position.

The second optical fiber preferably is arranged such that when theswitching member is in the first position, a portion of the secondoptical fiber is bent so that elastic forces in the first optical fiberretain it in the first position in the V-groove.

The second fiber alignment head preferably comprises anelectromechanical relay that includes a housing, apparatus for pivotallymounting the switching member in the housing, and apparatus arranged tolatch the switching member such that the first and second optical fiberends are selectively either in or out of alignment.

A fiber optic switching apparatus according to the present invention mayfurther comprise a third fiber alignment head that is substantiallyidentical to the first fiber alignment head. A third optical fiber ismounted in the V-groove in the third fiber alignment head with the thirdfiber alignment head being mounted to the second fiber alignment headwith their V-grooves in facing relationship. The first and third opticalfibers are arranged such that when the switching member is in its firstposition, the first and second optical fiber ends are aligned in theV-groove in the first fiber alignment head and when the switching memberis in its first position, the first and third optical fiber ends arealigned in the V-groove in the third fiber alignment head.

An appreciation of the objectives o f th e present invention and a morecomplete understanding of its structure and method of operation may behad by studying the following description of the preferred embodimentand by referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view of a 1×1 fiber optic switching apparatusformed according to the present invention showing an input fiberarranged to provide an optical signal to an output fiber;

FIG. 2 is a top plan view of t he apparatus of FIG. 1;

FIG. 3 is a cross sectional view of the apparatus of FIGS. 1 and 2 takenalong line 3--3 of FIG. 2;

FIG. 4 is a perspective view of the fiber optic switching apparatus ofFIGS. 1-3;

FIG. 5 is a side elevation view of the apparatus of FIG. 1 showing theinput and output fibers arranged to be parallel;

FIG. 6 is a side elevation view showing a 1×1 fiber optic switchingapparatus according to the present invention in its off configuration;

FIG. 7 is a cross sectional view showing the core and cladding of a beamexpanded single mode optical fiber;

FIG. 8 is an enlarged cross sectional view showing end-to-end alignmentof a pair of beam expanded single mode optical fibers;

FIG. 9 is a side elevation view of a 1×2 fiber optic switching apparatusformed according to the present invention showing an input optical fiberarranged to provide an optical signal to a first output fiber;

FIG. 10 is a cross sectional view taken along line 10--10 of FIG. 9; and

FIG. 11 is a side elevation view of the 1×2 fiber optic switchingapparatus showing the input fiber arranged to provide an optical signalto a second output fiber.

DESCRIPTION OF THE PREFERRED EMBODIMENT

This disclosure describes an apparatus and a method for making and usingan improved fiber optic switching or coupling apparatus for applicationssuch as cornmunications systems. Specific details are disclosed toprovide a through description of the invention. However, it will beapparent that the present invention may be practiced without thesespecific details. Well-known components of the fiber optic switchingapparatus according to the present invention are shown in simplifiedform, rather than in detail, to avoid unnecessarily obscuring theinvention.

FIG. 1 illustrates a fiber optic switching apparatus 10 according to thepresent invention. The fiber optic switching apparatus 10 is a 1×1switching apparatus having an on state and an off state. In the on statethe fibers 12 and 14 are aligned so that optical signals are directedfrom a signal input fiber 12 to a signal output fiber 14. In the offstate the fibers 12 and 14 are not in alignment so that optical signalsemitted from the end of the input fiber 12 are not directed to the endof the output fiber 14.

The position of the input fiber 12 is controlled by a relay 16. Therelay 16 preferably is a well-known type of relay widely used intelephone switching apparatus. As such, the relay 16 is formed to bemounted to a printed circuit board 18 to facilitate application ofcontrol signals from an electronic control circuit 20. Portions of thestructure of the relay 16 that are used in the present invention aredescribed below. It should be noted that the relay 16 is included in apresently preferred embodiment of the invention for controlling theposition of the input fiber 12. The invention is not limited to the useof the relay 16. The invention may be practiced with other apparatus forcontrolling position of the end 13 of the input fiber 12. It should benoted that drawings illustrating the relay 16 and other components ofthe invention are not scale. Dimensions of various components areadjusted to illustrate the principles of the invention.

The relay 16 includes a housing 22 that is formed generally as a hollowbox having rectangular sides. The length of the relay housing 22 isabout 14 mm and its height and width are about 8 mm and 10 mm,respectively. The relay 16 includes a switching member 24 formedgenerally as a thin elongate rectangle made of a ferromagnetic material.The central portion of the switching member 24 is mounted on a pivotingdevice 26 for pivoting movement between a pair of electromagnets 28 and30. The pivoting device 26 preferably is a generally rectangularpermanent magnet that extends into a similarly-shaped recess 31 in thecenter of a surface 32 of the switching member.

The typical structure of the relay 16 includes a thin rectangularinsulator 34 used to mount electrical conductors (not shown) to theswitching member 24. The insulator 34 extends a small distance above theplane of the rectangular switching member 24. The input fiber 12preferably is mounted to the insulator 34 and arranged to be parallel tothe length of the switching member 24.

Application of an electrical signal from the electronic control device20 to the electromagnet 28 attracts the end 36 of the switching member24 to the electromagnet 28 to place the switching member 24 and theinput fiber 12 in the "down" position shown in FIG. 1.

The output fiber 14 preferably is mounted in a V-groove 40 formedlengthwise in a fiber retainer 42. The fiber retainer 42 preferably isformed as a block having generally rectangular surfaces. The length ofthe fiber retainer is about 11 mm so that the total length of the fiberoptic switching apparatus 10 is about 25 mm. The height of the fiberretainer is about 8 mm, and its width is about 10 mm.

As shown in FIGS. 1 and 2, the output fiber 14 extends over aboutthree-fourths of the length of the V-groove 40. The output fiber 14 issecured in the V-groove by a suitable adhesive as is well-known inoptical fiber technology.

The electro-optical, electrical and mechanical and environmentalcharacteristics of the fiber optic switching apparatus 10 are summarizedin Tables I, II and III, respectively.

The input fiber 12 is mounted to the relay 16 so that the end of theinput fiber 12 extends into the V-groove 40 adjacent the end 15 of theoutput fiber 14 when the input fiber is in the down position of FIG. 1.When the ends of the input fiber 12 and the output fiber 14 are adjacentas shown in FIG. 1, optical signals will couple from the end 13 of theinput fiber 12 into the end 15 of the output fiber 14. The ends 13 and15 preferably are coated to reduce reflections. As shown in FIG. 1, theends 13 and 15 are cleaved at angles, which prevents any light that maybe reflected at the ends 13 and 15 from being propagated in the reversedirection in the input fiber 12.

A noteworthy feature of the fiber optic switching apparatus 10 is thatthe input fiber end 13 extends a few millimeters into the V-groove 40when the relay 16 is in the down position of FIG. 1. The input andoutput fibers are mounted such that when the relay 16 is in the downposition, the end 15 of the input fiber 12 is pressed into the V-groove40. When the input fiber 12 and output fiber 14 are parallel, the inputfiber 12 is displaced from the output fiber by a small distance as shownin FIG. 4. The fibers 12 and 14 are arranged so that when the inputfiber is lowered into the V-groove 40, the end segment of the inputfiber is aligned end-to-end with the output fiber 14 with elastic forcesin the fiber 12 applying a downward force to keep the end of the outputfiber 12 in the V-groove 40.

The input fiber 12 has two degrees of freedom when it is not in theV-groove 40. Mere placement of the input fiber 12 in the V-groove 40could allow the fiber end 13 to move away from the bottom of theV-groove 40 in response to vibrations or the like. Exerting a force onthe input fiber end 13 keeps it the desired position to maintainconstant signal transmission to the output fiber 14.

The present invention may be practiced with either ordinary opticalfiber or beam expanded fiber. FIG. 7 illustrates a modification of asingle mode optical fiber to improve end-to-end coupling. Referring toFIG. 7, an optical fiber 44 has a core 46 and a cladding 48. Because ofthe difference between core and cladding diameters, the optical fiber 44is not drawn to any scale. Optical signals are guided by the corebecause of total internal reflection at the core/cladding interface.

The core 46 is a germanium-doped region of the optical fiber 44 having anormal diameter of about 9 μm. The cladding diameter of a typical singlemode optical fiber is about 125 μm. The core diameter at a region 50 ofthe optical fiber 44 is expanded by applying heat thereto, which causesthe germanium dopant to migrate radially outward. It has been found thatapplication of heat with a microbuner to heat the core region 50 to atemperature of about 1250° C. for ten to fifteen minutes expands thediameter of the core region 50 to about 30 μm.

Heat is applied so that the core region 50 tapers at its ends 52 and 54.Tapering the ends 52 and 54 of the core region 50 causes optical signalsto propagate from the 9 μm diameter normal region of the core 46 to the30 μm a diameter region 50 without substantial end reflection.Therefore, there is virtually no loss of signal intensity when thediameter of the beam guided by the optical fiber 60 expands from 9 μm to30 μm.

The fiber 44 is then cleaved with an angled end facet along a line 56near the midpoint of the expanded core region 50. The fiber is cleavedalong an angle to minimize back reflection. For many sensitive fiberoptic systems back reflection can induce excessive noise and laserinstability. Cleaving the end of the fiber at an angle faces reducesbackward propagation of end face reflections. Properly choosing thecleave angle can reduce back reflections to less than -60 dB.

The process described above may be used to form the fiber end 13 in theinput fiber 12 and the end portion 15 of the output fiber 14. FIG. 8 isan expanded view of a portion of the alignment head 42 showing the inputoptical fiber end seμment 13 aligned with the output optical fiber end15. In the embodiment of FIG. 1, both of the optical fibers 12 and 14beam expanded single mode fibers of the type described above. The use ofbeam expanded fibers has significant advantages over normal single modeoptical fiber. One advantage is that light will propagate out of theinput fiber end 13 into the output fiber end 15 without requiring anylenses. Another advantage is that with a core diameter of 30 μm, thediameter of the beam output from the input fiber end 13 is sufficientlylarge that a lateral misalignment of about 6 μm is permissible.

FIG. 9 illustrates a 1×2 fiber optic switching apparatus 100 accordingto the present invention. The fiber optic switching apparatus 100includes the structure of FIGS. 1-4 in combination with a secondalignment head 102 and a second output fiber 104. The components of thefiber optic switching apparatus 10 that are included in the fiber opticswitching apparatus 100 have the same reference numerals as in FIGS.1-4. The printed circuit board 18 and electrical control device are notshown in the illustrations of the fiber optic switching apparatus 100.It is to be understood that all embodiments of the present invention aredesigned to be used with some type of electrical control apparatus, thedetails of which are not a part of the invention.

Referring to FIGS. 9-11, the second fiber alignment head is formed to beessentially identical to the first alignment head 42. The second outputfiber 104 is secured within a second V-groove 106. The second outputfiber 104 preferably has a beam expanded end portion 108. The firstfiber alignment head 42 and the second fiber alignment head 102 areconnected together so that the V-grooves 40 and 106 are parallel andfacing one another. An adhesive preferably is used to connect thealignment heads together.

The 1×2 fiber optic switching apparatus 100 may be actuated to provideoptical signals from the input fiber 12 to a selected one of the outputfibers 14 or 104. Application of an electrical signal to theelectromagnet 28 causes the switching member 24 to move the "down"position shown in FIG. 9 to align the input fiber end 13 with the outputfiber end 15. In a latching embodiment of the invention, theelectromagnet 28 has a residual magnetism sufficient to retain the end36 of the switching member 24 in the down position in the absence of anycontrol signal.

Application of a control signal to the electromagnet 30 causes theswitching member 24 to pivot about its support to place the switchingmember 24 in an "up" position shown in FIG. 11. When the switchingmember is in the up position, the end 37 of the switching member 24contacts the electromagnet 30. The residual magnetism of theelectromagnet 30 latches the switching member 24 in the up position.

The second output fiber 104 is arranged in its V-groove 106 so that whenthe switching member 24 is in the up position, the input fiber end 13 ispressed into the V-groove 106 in the manner described previously withreference to the input fiber end 13 and the V-groove 40. As describedpreviously, the input fiber 12 has a curved portion just outside theV-grooves 40 and 106 so that elastic forces in the fiber 12 retain theend 13 in contact with the sides of the V-groove 106 when the switchingmember 24 is in the "up" position. Therefore, application of control, orswitching, signals to the relay 16 switches the optical output of thefiber optic switching apparatus 100 between the output fibers 14 and104.

                  TABLE I                                                         ______________________________________                                        Electro-Optical Characteristics                                               PARAMETER      1 × 1 Switch                                                                          1 × 2 Switch                               ______________________________________                                        Wavelength range (nm)                                                                        1280-1650     1280-1650                                        Insertion Loss (dB), max.                                                                     1             1                                               Return Loss (dB), typ.                                                                       60            60                                               Crosstalk (dB), min.                                                                         60            60                                               Switching Speed (ms), max.                                                                    4             4                                               Repeatability (dB), min.                                                                     0.1 (>10.sup.7 cycles)                                                                      0.1 (>10.sup.7 cycles)                           ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        Electrical Characteristics                                                    PARAMETER          1 × 1 Switch                                                                      1 × 2 Switch                               ______________________________________                                        Coil Resistance, (Ω)                                                                       90-250    90-250                                           Operating Current (mA), max.                                                                      34        34                                              Power Consumption (mW), max.                                                                     100       100                                              ______________________________________                                    

                  TABLE III                                                       ______________________________________                                        Mechanical & Environmental Characteristics                                    PARAMETER  1 × 1 Switch                                                                           1 × 2 Switch                                  ______________________________________                                        Op. Temp. Range                                                                          -40 to +85     -40 to +85                                          (° C.)                                                                 Relative Humidity                                                                        35 to 85%      35 to 85%                                           Fiber Pigtail                                                                            φ 0.9 mm (SM, 10/125)                                                                    φ 0.9 mm (SM, 10/125)                           Dimensions (mm ×                                                                   25 (L) × 8 (H) × 10 (W)                                                          25 (L) × 8 (H) × 10 (W)                 mm × mm)                                                                ______________________________________                                    

The structures and methods disclosed herein illustrate the principles ofthe present invention. The invention may be embodied in other specificforms without departing from its spirit or essential characteristics.The described embodiments are to be considered in all respects asexemplary and illustrative rather than restrictive. Therefore, theappended claims rather than the foregoing description define the scopeof the invention. All modifications to the embodiments described hereinthat come within the meaning and range of equivalence of the claims areembraced within the scope of the invention.

What is claimed is:
 1. A fiber optic switching apparatus, comprising:afirst fiber alignment head having a V-groove formed therein; a firstoptical fiber mounted in the V-groove with an end of the first opticalfiber being arranged to be spaced apart from an end of the V-groove; asecond fiber alignment head arranged to be adjacent the first fiberalignment head, the second fiber alignment head including a switchingmember that is arranged to be pivotable between a first position and asecond position; and a second optical fiber connected to the switchingmember, the second optical fiber, the switching member and the V-groovebeing aligned such that when the switching member is in the firstposition a portion of the second optical fiber is bent such that elasticforces retain an end thereof in the V-groove such that the ends of thefirst and second optical fibers are in longitudinal alignment when theswitching member is in its first position and are out of alignment whenthe switching member is in its second position.
 2. A fiber opticswitching apparatus, comprising:a first fiber alignment head having aV-groove formed therein; a first optical fiber mounted in the V-groovewith an end of the first optical fiber being arranged to be spaced apartfrom an end of the V-groove; a second fiber alignment head arranged tobe adjacent the first fiber alignment head, the second fiber alignmenthead including a switching member that is arranged to be pivotablebetween a first position and a second position; a second optical fiberconnected to the switching member, the second optical fiber beingarranged to have an end extending into the V-groove such that the endsof the first and second optical fibers are in longitudinal alignmentwhen the switching member is in its first position and are out ofalignment when the switching member is in its second position; andwherein the second fiber alignment head comprises an electromechanicalrelay that includes a housing, apparatus for pivotally mounting theswitching member in the housing, and apparatus arranged to latch theswitching member such that the first and second optical fiber ends areselectively either in or out of alignment.
 3. A fiber optic switchingapparatus, comprising:a first fiber alignment head having a V-grooveformed therein; a first optical fiber mounted in the V-groove with anend of the first optical fiber being arranged to be spaced apart from anend of the V-groove; a second fiber alignment head arranged to beadjacent the first fiber alignment head, the second fiber alignment headincluding a switching member that is arranged to be pivotable between afirst position and a second position, and an electromechanical relaythat includes a housing and apparatus for pivotally mounting theswitching member in the housing; a second optical fiber connected to theswitching member, the second optical fiber, the switching member and theV-groove being aligned such that when the switching member is in thefirst position a portion of the second optical fiber is bent such thatelastic forces retain an end thereof in the V-groove such that the endsof the first and second optical fibers are in longitudinal alignmentwhen the switching member is in its first position and are out ofalignment when the switching member is in its second position; andapparatus arranged to latch the switching member such that the first andsecond optical fiber ends are selectively either in or out of alignment.4. The fiber optic switching apparatus of claim 3, further comprisingelectronic control means arranged for controlling the apparatus arrangedto latch the switching member.
 5. The fiber optic switching apparatus ofclaim 4 wherein the apparatus arranged to latch the switching memberincludes a pair of magnets arranged for moving the switching member to aselected position for controlling alignment of the first and secondoptical fibers.
 6. A fiber optic switching apparatus, comprising:a firstfiber alignment head having a first V-groove formed therein; a firstoptical fiber mounted in the first V-groove with an end of the firstoptical fiber being arranged to be spaced apart from an end of the firstV-groove; a second fiber alignment head arranged to be adjacent thefirst fiber alignment head, the second fiber alignment head including aswitching member that is arranged to be pivotable between a firstposition and a second position; a second optical fiber connected to theswitching member, the second optical fiber being arranged to have an endextending into the first V-groove such that the ends of the first andsecond optical fibers are in longitudinal alignment when the switchingmember is in its first position and being out of alignment when theswitching member is in its second position; a third fiber alignment headthat is substantially identical to the first fiber alignment head andhaving a second V-groove therein; and a third optical fiber mounted inthe second V-groove, the third fiber alignment head being mounted to thesecond fiber alignment head with the first and second V-grooves infacing relationship, the first and third optical fibers being arrangedsuch that when the switching member is in its first position, the firstand second optical fiber ends are aligned in the first V-groove and whenthe switching member is in its second position, the first and thirdoptical fiber ends are aligned in the second V-groove.
 7. The fiberoptic switching apparatus of claim 6 wherein the second optical fiber isarranged relative to the first and third optical fibers such thatelastic forces in the second optical fiber retain it in the firstV-groove when the switching member places the first and second opticalfibers in alignment and retain the second optical fiber in the secondV-groove the switching member places the first and third optical fibersin alignment.